Being a toner, milk lotion, and essence
It feels light enough to be all three of them.

Claims to be a whitening essence
I always take this with a grain of salt. To date, I've only come across 2 products that visibly whitens / brightens. One of them is the Paul & Joe Whitening Serum, and the other is the TonyMoly Tomatox Magic White Massage Pack. I haven't noticed any difference to the color of my skin while using the Mizuno Tenshi Flower Moisture Gel. My age and acne spots are still there and the same dark/light -ness. But I can't say for sure that this product isn't doing something in this department. I'm not willing to say it does or it doesn't whiten...it's just too hard and miniscule to really tell.

Can be used as a makeup base

It absorbs so completely and dries matte. I've used it under makeup and haven't had any issues with it.

Relieves dry, dull and rough skin

This statement is true if your skin was dry, dull, and rough before you applied this Flower Moisture Gel. However, you will still need an exfoliation regimen. This product will not cure everything.

Restores skin's luminosity and moisture
Only as far as initial application goes. I haven't noticed my skin becoming more luminous from using this alone. I've acquired the luminous effect only after exfoliation. As far as moisture goes, for my face, this is moisturizing enough for the warmer months. However, no matter what time of year it is, I don't think it will be moisturizing enough around the eyes. You will need a heaver product for the eye area.

Suitable for all skin types, and dry and delicate skin
I honestly can't see how this will be moisturizing enough for dry and delicate skin. For my oily skin, this is perfect. But I think for people with naturally drier skin, I think they will want something heavier.

What are my thoughts?
I think if you wanted to use this as a summer-time light moisturizer, by all means go ahead! But I don't think you should expect too much out of it. Thank goodness I got this 40% off! If I repurchase this at all, the purpose would only be to moisturize in the summer. Other than that, I probably won't repurchase.